Auto merge of #972 - bitcartel:zc.v0.11.2.z3_issue_651_remove_bitcoin_seeds, r=ebfull
Auto merge of #972 - bitcartel:zc.v0.11.2.z3_issue_651_remove_bitcoin_seeds, r=ebfull

Remove Bitcoin mainnet and testnet seeds.

Simple patch for issue #651 to remove hard-coded mainnet and testnet seeds
- they currently point to bitcoin nodes
- some are .onion addresses but Tor support has not yet been added
- gets rid of error messages in debug.log which might confuse people testing the alpha builds

bitcoinsSG/zcash,CTRoundTable/Encrypted.Cash,aniemerg/zcash,bitcoinsSG/zcash,bitcoinsSG/zcash,CTRoundTable/Encrypted.Cash,bitcoinsSG/zcash,CTRoundTable/Encrypted.Cash,bitcoinsSG/zcash,CTRoundTable/Encrypted.Cash,aniemerg/zcash,CTRoundTable/Encrypted.Cash,aniemerg/zcash,aniemerg/zcash,aniemerg/zcash,CTRoundTable/Encrypted.Cash,aniemerg/zcash,bitcoinsSG/zcash